There is well known a joining device provided in a tire molding apparatus, configured to overlap end portions of a rubber member, e.g., a tire constituent member on a molding drum vertically, that is, with one of the end portions positioned outside in a radial direction of the tire molding drum and the other positioned inside in the radial direction thereof, press a pressing roll against the overlapped portion, and join the end portions together (for example, see Patent Literature 1).
FIG. 9 is a perspective view schematically illustrating a principle of such joining of the tire constituent member.
In this conventional joining device for tire constituent member, a tire constituent member 100 made of a rubber material and having a predetermined length is wound around a molding drum with end portions 101 and 102 thereof overlapped with each other vertically, and a pressing roll 110 is rolled on and presses the overlapped portion. This allows the end portions 101 and 102 of the tire constituent member 100 to be joined together by utilizing adhesiveness of an unvulcanized rubber, thereby forming a cylindrical body such as a carcass ply.
In such a case where both end portions of the tire constituent member are overlapped, and the pressing roll 110 presses the overlapped portion from above to join them, as a matter of course the smaller (or narrower) an amount of the overlap (joining area) is, the lower joint strength thereof becomes. Thus, there is a problem that required joint strength cannot be maintained unless a certain joining area is ensured.